TLDR: Sekiro is not difficult for the sake of being difficult. The experience it provides requires players to have a certain level of mastery of gameplay mechanics (e.g. deflection and exploiting the posture system) -- this is what makes it difficult. This argument applies to any of the other Soulsborne titles, too.
Buckle in because this is gonna be a long one.
To play Sekiro, you really have embrace the mindset of a motherfucking NINJA. Having difficulty settings wouldn't make sense because it would result in an altogether different experience. However, for the sake of the argument let's consider tweaking different aspects of the game that might make it more accessible.
You could slow down enemy attack animations. When fighting against samurais, shinobis, and other individuals in world that places a large emphasis on swordsmanship and hand-to-hand combat, it wouldn't make any sense for the player to always be quicker than his enemies. Sekiro is incredibly fast, but so are his opponents. Besting your opponents requires skill and quick reactions... like a ninja. One of the best moments in the game is when the player becomes painfully aware of their own growth in skill and those enemies that gave you so much trouble at the beginning of the game get absolutely destroyed if you encounter them later on (e.g. Lone Shadow Longswordsman and Juzou the Drunkard). Hesitation is defeat.
You could make enemies less aggressive. This kinda ties into the whole ninja experience I keep referring to. Engagements in Sekiro are meant to be quick and brutal. Enemy aggression forces the player into battle of quick wit and skillful swordplay. Also, you aren't meant to take on large groups of enemies at the same time; stealth tactics help you wittle down groups until you get to focus on one-on-one duels.
You could have enemies deal less damage. This would be the easiest thing to tweak, but would detract from the emphasis placed on quick and brutal gameplay. Also, swords are meant to be lethal and enemies should be able to kill you as quickly as you can kill them. In my honest opinion, I hate damage sponges and people that just try to tank everything.
You could place less emphasis on the posture system. Have you seen Sekiro's katana? It's tiny. Have you seen the enemies he goes up against? They're huge. Sekiro isn't meant to block everything hence the emphasis on deflection and posture damage. You want the fights to be over quickly so you need to attack aggressively and overwhelm an enemies posture to get that sweet, sweet deathblow. Also, those big dudes aren't gonna go down easy unless you cripple their posture recovery by getting in some attacks to their vitality here and there. Soley focusing on chipping at an opponents health will cause a fight to drag and should be a huge indicator that you aren't approaching things correctly.
You could widen the timing window for deflections. The window for deflections has been expertly tuned in my opinion. If they make it any wider then you rob the player of the sense of accomplishment they feel when they actually pull off a perfectly timed deflection.
To those people who bought the game and can't come to grips with its difficulty... Newsflash: FromSoftware titles are notoriously difficult. If you knew that going in then I can assume that you're probably getting your ass handed to you because you're trying to play the game like a Soulsborne game (e.g. dodge or sidestep to victory). The game explicitly punishes the style of play. Mastering deflection and the posture system is absolutely key to finishing this game. Genichiro is the first wall in the game that absolutely forces players to come to terms with this fact.
As for being elitist/snobby about difficulty in video games... With respect to Sekiro, maybe I just get annoyed when a game of this style and quality is rare to come by and then a bunch of people complain that the game can't be made to exactly suit their desires and/or are too lazy to actually play the game in its intended way. Sekiro isn't a game for that type of person and catering to accessibility would undermine almost everything the game does. The reason why FromSoftware's game are so damn good is because they don't give a damn if everyone will like their games -- they have faith in themselves and are confident in the experiences they embrace in their titles.
God of War is great game and is accessible to a lot of people. I play God of War when I want to experience being a freaking god and live out a power fantasy without really having to try. I play Sekiro when I want to be a master shinobi and actually feel like I earned that description.